Holograms with discontinuous metallization including alpha-numeric shapes

ABSTRACT

Non-continuous reflective hologram or diffraction grating devices are provided in various forms for authenticating documents and things, such as those that contain visual information desired to be protected from alteration. Examples of such information include written personal data and photograph on a passport, driver&#39;s license, identity card, transportation pass, and the like. The reflective discontinuous hologram or diffraction device is formed in a pattern that both permits viewing the protected information through it and the viewing of an authenticating image or other light pattern reconstructed from it in reflection. The same master hologram or diffraction grating is made into distinct authentication devices by forming replicas thereof that have different patterns of reflective material which form distinct indicia, such as a different alpha-numeric character.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is related to application Ser. No. 07/291,247, filed Dec. 23, 1988,which is a continuation-in-part of application Ser. No. 07/160,641,filed Feb. 26, 1988, now abandoned, and which in turn is acontinuation-in-part of application Ser. No. 07/156,305, filed Feb. 12,1988, now abandoned. A corresponding European patent application no.89102182.6 was published Aug. 16, 1989 as no. 328,086, and isincorporated herein by this reference.

BACKGROUND OF THE INVENTION

This invention relates generally to the optical arts of holography anddiffraction gratings, and more particularly, to a special forms of theseoptical devices for use in authenticating documents and other items asgenuine.

There is a wide-spread need to authenticate written information andarticles in order to prevent both the counterfeiting of the article andan alteration of a genuine article. Examples of such articles includecredit cards, identification cards, driver's licenses, transit passes,passports, stock certificates, and the like. Holograms are currentlybeing extensively used on credit cards and transit passes, for example.An image having observable three-dimensional characteristics is viewablein light reflected from such a hologram.

Because holograms are difficult to make and require a high level oftechnical sophistication, the difficulty of making a counterfeit creditcard, or other article to which a hologram is attached, is increased. Amaster hologram is made in an optical laboratory with coherent light.The resulting master hologram is capable of reconstructing an image ofthe object from which it is made. Low-cost replicas are then made fromthat master. Several specific replication techniques are known, the mostcommon currently being to make the master in a manner that the objectinformation is stored in a surface relief pattern. This surface reliefpattern is then used to make replicas by an embossing or castingoperation. A layer of reflective material is applied to each replicasurface relief pattern so that the image may be viewed in lightreflected from that pattern. The holograms are then firmly attached tothe credit card or other article to be authenticated. The hologram isalso constructed of suitable materials so that an attempt to remove thehologram from the article will destroy it, thereby eliminating thepossibility of a counterfeiter transferring a hologram from a genuinearticle and onto a counterfeit article.

An authenticating hologram of this type cannot cover printing,photographs and the like carried by the article to be authenticated whenthat information wants to be viewed. This is because the reflectivelayer of the hologram is substantially opaque so that any visualinformation on the article in the area to which it is attached iscovered by the hologram. Some credit cards are authenticating some ofthe raised alpha-numeric information on them by covering at least a fewof the characters with the hologram. But any printing, photographs orthe like on a flat surface under the hologram is not viewable.

There has been some effort to control the amount of reflective materialthat is applied to the surface relief hologram so that it will bothreflect enough light in order to reconstruct an image recorded in thehologram and at the same time be transparent enough to make visible anyprinting, photograph or other visual information under the hologram.Besides authenticating the article to which the hologram is attached andthe visual information under it, such a

hologram has the potential of preventing alteration of that informationon an authentic article. It has been found to be very difficult,however, to be able to repeatedly form a reflective layer on thehologram that gives it these advantageous characteristics. Aluminum isusually employed as the reflective material. A proper thickness of thatlayer can result in the desired partial transparency and partialreflection, but the processes used to date have been very difficult tocontrol in order to provide the proper thickness.

Holograms are also being used to authenticate documents, such as transitpasses, that are reissued at frequent periodic intervals, such asmonthly. It is often desired that the hologram be changed each month sothat transit authorities can easily recognize a valid current transitpass from an expired one. This presently requires making a new opticalmaster hologram for each new pass, an expensive and time consumingprocess.

Therefore, it is a specific object of the present invention to providean improved hologram or diffraction grating for attaching to a documentor article over visual information that is to be protected, wherein theinformation can be observed through the hologram and an imagereconstructed from the hologram may be observed.

It is another object of the present invention to provide anauthentication hologram or diffraction grating, and process for makingit, that allows easy modification for monthly transit passes and thelike without having to make a new optical master.

It is a more general object of the present invention to provide novelholograms and diffraction gratings for authentication of documents andother articles.

SUMMARY OF THE INVENTION

These and additional objects are accomplished by the articles andprocesses of the present invention, wherein, briefly, a continuoushologram or diffraction grating device is provided from which an imageor other recognizable pattern is reconstructed in light reflected fromthe device but light reflective material is discontinuously provided indistinctive shapes such as one or more alpha-numeric characters. Thereflective material pattern can thus be selected to convey informationwhich is independent of that recorded on the hologram or diffractiongrating. In the case of transit passes discussed above, for example, thesame hologram or diffraction grating can be used for each month's pass,the pattern of reflective material clearly indicating the current monthfor which the pass is valid. This technique is optimally combined with anoncontinuously reflective hologram or diffraction pattern that coversinformation on a substrate to be protected but the technique can also beused as part of an otherwise solid hologram that is attached to asubstrate along side information desired to be visible.

Additional objects, advantages and features of the various aspects ofthe present invention will become apparent from the followingdescription of the preferred embodiments thereof, which descriptionshould be taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an article having visual information that isprotected by an improved hologram of the present invention beingattached thereto;

FIG. 2 is an expanded view of a portion of the protected article of FIG.1;

FIG. 3 is a cross-sectional view of the structure of FIG. 2 taken acrosssection 3--3 thereof;

FIG. 4 is an expanded view of another portion of the protected articleof FIG. 1;

FIG. 5 is a cross-sectional view of the structure of FIG. 4, takenacross section 5--5 thereof;

FIG. 6 illustrates a continuous process for making a hologram ordiffraction grating of a type used to authenticate an article, such asshown in FIG. 1;

FIGS. 7 and 8 show individual components used in the process of FIG. 6;and

FIGS. 9-12 shows some alternative structures of a hologram ordiffraction grating made according to the process illustrated in FIGS.6-8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1, an example is given of an article havinga protective hologram attached that utilizes the present invention. Adocument, such as a passport, driver's license, personal identificationcard, transit pass, or the like, includes a photograph 11 of the bearer.Written information 13 of the bearer is also provided on the surface ofthe document. The document can be paper, plastic or some other materialthat contains visual information to be protected from alteration.Covering at least the photograph 11 and the written information 13 is asee-through hologram authentication device of a type discussed in thepatent applications cross-referenced above. Such a hologram reconstructsin reflected light images recorded in it, such as reconstructed images15. Thus, the information 11 and 13 to be protected is covered with ahologram that allows the information to be observed through it at thesame time as allowing the authenticating reconstructed images 15 to beobserved.

A small area 17 of FIG. 1 is expanded in FIG. 2. FIG. 3 shows asectional view through the expanded portion of FIG. 2. A hologram 19 isattached to a substrate 21 by an appropriate adhesive layer 20. Thehologram 19 includes a substantially clear plastic film 23 having asurface relief pattern 25 formed on an inside surface thereof. Thesurface relief pattern 25 is continuous across at least a defined areaof the hologram 19, continuing over the entire hologram in this exampleand thus the entire protected document. The surface relief pattern isformed from a master hologram by a standard embossing or castingtechnique.

That portion of the surface relief pattern 25 to which a reflectivelayer is attached will be operative in reflecting incident light intothe recorded image or other light pattern. In the hologram portionillustrated in FIGS. 2 and 3, reflective aluminum dots 27 areperiodically spaced across the surface relief pattern 25 and attached toit in a manner to follow its contours. As described in considerably moredetail in the applications cross-referenced above, this allows an imageto be reconstructed from the hologram 19 in reflected light at the sametime as the photograph 11 and other information attached through thesubstrate 21 is viewed through the hologram. The opaque, reflective dots27 are made of a size and spaced apart sufficient for this to occur.

In addition to the reflective dots, the opaque metallization of thehologram surface relief patter in the embodiment of FIG. 1 is configuredover an area of the protected document not covering the photograph 11 orother information 13 to provide a unique indicia that is separate,independent and unregistered from the images 15 reconstructed from thehologram. The indicia formed by the hologram metallization pattern isalso separate and independent from the document information 11 and 13being protected. In this case, that indicia is alphanumeric information,namely a month 29 and a year 31. The information or visual design of theprotected document itself can also be changed each time that thehologram metallization pattern characters are changed but this techniqueallows use of other copies of the same document without change, ifdesired, for economics and simplicity.

FIG. 4 shows an expanded view of another small area 33 of the protecteddocument of FIG. 1. This includes a portion 35 of the "nine" of the year31 that is visible from the face of the protected document of FIG. 1.The number is formed by the shape of the reflective metallization layerthat is applied to the surface relief pattern 25. The region 33 shown inFIG. 4 illustrates that metallization pattern to retain the reflectivedots around it. The metallization 35 also provides a reflective backingfor reconstructing an image from the hologram surface relief pattern 25covered by it.

This information can be a month and year of expiration of the protecteddocument, of a month during which the protected document is valid, andthe like. In such cases, new documents need to be issued periodicallyand it is quite expensive if an entirely new protective hologram needsto be constructed for use with each document reissue. What is mostexpensive is the making of an optical master hologram. But the techniqueof adding the indicia 29, 31 in a metallization step allows the sameauthenticating hologram to be utilized in successive reissues of thedocument since the metallization step occurs after the hologramreplication step. A large number of such protective holograms can bemanufactured for inventory with limited amounts periodically withdrawnand metallized with unique indicia 29, 31, but it generally ispreferable to replicate each new issue of the protective hologram fromthe beginning. This still utilizes the same master hologram replicatingplates for each issue, only the pattern of metallization changing. Nonew optical hologram master need be made.

Such a technique is illustrated generally in FIGS. 6-8. FIG. 6illustrates the process steps for forming hologram replicas on acontinuous length of flexible substrate material 111. There are severaldistinct processing stages through which the web 111 passes. A firststage 113 applies liquid resin to defined areas of the web 111.Solidified, surface relief holograms are formed at station 115 in theseresin areas. Next, the web proceeds to a station 151 that prints aliquid onto the surface of the replica holograms in regions wherereflective material is not to be attached. A next station 153 applies areflective metal layer over the entire hologram replica surface reliefpattern. A station 155 then removes the metallization layer from thoseareas that were printed at station 151 with a liquid material. Next, atstation 157, the process web is dried and, at an optional station 159, aprotective coating and/or adhesive layer is placed on the metallizedsurface relief pattern.

Details of the hologram replica casting stations 113 and 115 can be hadfrom copending patent application Ser. No. 399,812, filed Aug. 29, 1989,the disclosure of which is incorporated herein by this reference.Briefly, a liquid bath 117 of casting resin has a first cylindricalroller 119 rotating about its axis through the liquid. The roller 119transfers such liquid to outward surfaces of pads, such as pads 125 and127, that are attached to an otherwise smooth cylindrical surface 123 ofa drum shaped roller 123.

A third roller 131 in the station 113 guides the web 111 in a path thatresults in contact between the pad surfaces of the roller 123 and theweb without any relative motion therebetween. Guide rollers 133 and 135also determine the paths of the web 111. Thus, liquid resin is appliedfrom the bath 117 to discreet areas of the web 111 as defined by thesize and pattern of the pads carried by the roller 123.

After leaving the station 113, the web 111 is passed in contact with theoutside of the cylindrical drum 137 by appropriate guide rollers 139 and141, in the second work station 115. The drum 137 has a plurality ofindividual hologram masters, such as pieces 143 and 145, attached to itsoutside surface. This arrangement is further shown in FIG. 7. Thesehologram master pieces are arranged essentially in the same pattern asthe pads of the drum 123. Rotation of the drums in the work stations 113and 115 is coordinated by a master control 147 to cause the individualhologram pieces 143, 145, etc. to contact areas of the web 111 that havebeen coated with liquid resin by the pads 125, 127, etc.

The web 111 and the hologram masters attached to the outside surface ofthe drum 137 move together without any motion between them. Liquid resinis held between each of the surface relief master holograms 143, 145,etc. and the web. While being so held, the liquid resin is hardened bycuring with actinic radiation. A source 149 of such radiation directs itthrough the web 111 to the trapped liquid resin. By the time a point onthe web has advanced to the position of the roller 141, the liquid resinhas been cured with the desired surface relief pattern formed therein.The web 111 is separated from the hologram masters 143, 145, etc. atthis point and proceeds to a next work station 151.

The station 151 then coats each of the hologram replicas with a liquidmaterial in a pattern of the desired non-continuous reflectivemetallization layer on the completed hologram. The web is directedaround a drum shaped roller 161 and is guided away from it by rollers163 and 165. A bath 167 of the liquid to be printed onto the hologramreplicas is a water soluble resin, such as polyvinyl alcohol. Thisliquid is transferred by a roller 169 to the outer surface of a roller171 which is urged into contact with the web against the roller 161. Ascan be seen from FIG. 8, a cylindrical surface of the printing drum 171contains a pattern 173 that corresponds with the desired pattern ofmetallization on the resulting hologram replica shown in FIG. 1. In thiscase, the pattern 173 for a single hologram is constructed so that theliquid 167 is applied to all areas of the cast hologram relief patternexcept for the regions of the desired metallization pattern 173. That isbecause the water soluble resin being applied will, in a subsequentstep, simply be washed away and thus will remove any reflective materialfrom the areas where the resin has been printed. The roller 171 ispreferably formed from a gravure cylinder having liquid containing holesformed in a negative of the desired metallization pattern for thehologram replicas.

After application of the water soluble resin at the work station 151,the web 111 proceeds to a station 153 that coats the entire web on itsside where the holograms are formed with an opaque, reflective materiallayer. That layer is preferably made of aluminum and the work station153 is preferably a standard vacuum metallization machine.

Next, the web 111 advances to a station 155 which submerses themetallized hologram replicas in a water bath. The metal layer issufficiently porous to allow water to penetrate through to the resin,thereby causing the resin applied at the station 151 to dissolve and thealuminum layer coated on such a resin to then be washed away. The nextwork station 157 simply dries the web by use of heat lamps and the like.Specific techniques and materials for use in the non-continuousmetallization process of stations 151, 153, 155 and 157 are given inU.S. Pat. Nos. 3,935,334--Narui et al. (1976) and 4,242,378--Arai(1980).

As an alternative to using a water soluble resin, a resin soluble in anyone of a wide variety of organic solvents can be printed onto the web111 prior to metallization. The metal layer is then removed in thepattern of the resin by submersing the coated web into a bath of theappropriate organic solvent.

A final, optional work station 159 uniformly coats the metallizedhologram replicas of the web 111 with a protective or adhesive layerfrom a liquid 174. A transfer roller 175 carries the liquid to the web111 surface. The web 111 is guided by another roller 177. After anappropriate drying step, the metallized hologram replicas have such adesired additional layer. The web is then ready for separation intoindividual holograms by die cutting and the like for attachment to adocument or other substrate surface to be protected. If it is desired toapply the individual holograms by a hot stamping process, the web 111 isthen alternately attached by a hot melt adhesive to a flexible plasticcarrier.

The example of the unique indicia 29, 31 (FIG. 1) formed during thereflective metallization step was described to be formed of solidreflective material. It is not necessary, however, that the alphanumericcharacters be solid. That is only one of many specific implementations.Four additional specific implements are illustrated in FIGS. 9-12 forrepresenting the letter "T" in the pattern of aluminization.

Referring initially to FIG. 9, a regular pattern of metallized dots 181exists on the surface relief hologram replica. The letter "T" is formedby omitting dots in the region 183. This technique works well in caseswhere the size of the individual dots and the density of the backgroundpattern 181 are clearly visible. The dot pattern can be made to bepractically invisible to the ordinary user but still reconstructholographic images, but in the case of FIG. 9, such an invisible patternof dots is not workable. The example of FIG. 9 has an advantage of beingable to place the "T" character 183 over information to be protected,such as the photograph 11 or writing 13 (FIG. 1), if desired, since noneof the protected document is blocked by it.

FIG. 10 is an example similar to FIG. 9 except that the region 183without a dot pattern is outlined in a thin continuous metal pattern185. This makes the letter "T" highly visible, even when the individualdots of the background pattern 181 may not be very visible, but does sowithout blocking view of much area of an underlying document to whichthe hologram is attached.

FIGS. 11 and 12 utilize the fact of a background pattern 181 of dotsclearly visible. The letter "T" is formed in FIG. 11 by a pattern 187 ofreflective dots that are larger than those of the regular backgroundpattern 181. The pattern of the dots 187 is the same as that of thebackground dots 181 but they are more dense and thus the pattern isdistinguishable from the background. The pattern 189 in FIG. 12 is madeto be different from the background pattern 181, and distinguishablebecause of that feature. The density of the area covered by dots in thepattern 189 may be the same as that of the background pattern 181.

The examples described above result in the making of a large number ofhologram replicas with the same alpha-numeric characters formed in themetal layer of each. Alternatively, these characters can be formed byuse of a printing technique that places a unique pattern on eachhologram replica. This is useful, for example, where each hologramreplica of a large batch of replicas is to carry a unique identifyingserial number that is clearly visible in the metal layer. This can beaccomplished by jet or laser printing techniques, by use of amechanically indexed print head included as part of the drum 171, etc.,to form a soluble layer pattern that is somewhat different for eachreplica.

Although the various aspects of the present invention have beendescribed with respect to their preferred embodiments, it will beunderstood that the invention is entitled to protection within the fullscope of the appended claims.

It is claimed:
 1. A document having visual information thereon protectedfrom alteration, comprising a hologram or diffraction grating devicefirmly attached to said document over at least a portion of said visualinformation, said device comprising:a substantially transparent layerhaving a surface relief pattern formed in a surface thereof facing thedocument and its said visual information with substantially completelyreflective material attached thereto in a discontinuous patternthereacross in a manner that the device, when illuminated with light,allows viewing of both the visual information on the document throughsaid layer and a light image or pattern reconstructed from said surfacerelief pattern in reflection from portions thereof to which saidreflective material is attached, and said reflective materialadditionally being arranged in a shape or pattern of visual informationseparate from that of the reconstructed image or pattern and alsoseparate from the document visual information.
 2. The combination ofclaim 1 wherein the visual information conveying arrangement of thereflective material includes one or more substantially solidalpha-numeric characters.
 3. The combination of claim 1 wherein thevisual information arrangement of the reflective material is formed by asecond discontinuous pattern thereof distinct from the surroundingdiscontinuous pattern and in a shape of one or more alpha-numericcharacters.
 4. The combination of claim 1 wherein the visual informationarrangement of the reflective material is formed by omitting thediscontinuous pattern thereof in a shape of one or more alpha-numericcharacters.
 5. The combination of claim 5 wherein the omitteddiscontinuous pattern of reflective material is further outlined in saidreflective material in a manner to form said one or more alpha-numericcharacters.
 6. The combination of any one of claims 1 to 5 wherein thedevice surface relief pattern is continuous over said at least a portionof the visual information and wherein the reflective material isprovided as a layer attached to said surface relief pattern.
 7. Thecombination of either of claims 1 or 2 wherein the visual informationarrangement of the reflective material is substantially non-overlappingwith the document visual information, thereby not interfering therewith.8. The combination of any one of claims 1, 3, 4, or 5 wherein the visualinformation conveying arrangement of the reflective material at leastpartially overlaps with the document visual information.
 9. Thecombination of claim 1 wherein said discontinuous pattern of reflectivematerial includes at least an area of a regular pattern of dots of agiven size and a given density, and further wherein said reflectivematerial visual information includes at least one alpha-numericcharacter formed within said regular pattern area with a density and/orsize of dots therein that is visually distinct from that of thesurrounding regular pattern of dots.
 10. The combination of claim 9wherein said at least one alpha-numeric character at least partiallyoverlaps with the document visual information.
 11. A combination,comprising:a substrate having visual information thereon, asubstantially transparent hologram or diffraction grating device layerfirmly attached to said substrate in a manner to protect at least aportion of said information from alteration, said device layercharacterized by forming a recognizable image or other light pattern inlight reflected therefrom, a discontinuous pattern of substantiallyopaque reflective material positioned between said device layer and saidsubstrate over a region of said visual information in a manner to allowsimultaneous viewing of (1) said region of visual information throughsaid device layer and said discontinuous pattern and (2) said image orother light pattern formed in light reflected from portions of thedevice layer covered with said reflective material, and at least onealpha-numeric character formed by an arrangement of said substantiallyopaque reflective material positioned between said device layer and saidsubstrate and viewable through the device layer.
 12. The combination ofclaim 11 wherein said at least one alpha-numeric character is formed ofsaid reflective material in solid form.
 13. The combination of claim 11wherein said at least one alpha-numeric character is formed by avisually distinct second discontinuous pattern.
 14. The combination ofclaim 11 wherein said at least one alpha-numeric character is formed byomitting the discontinuous pattern thereof in a shape of said at leastone alpha-numeric character.
 15. The combination of claim 14 wherein theomitted discontinuous pattern is further outlined in said reflectivematerial in the shape of one or more alpha-numeric characters.